Various kinds of water pressure reducing valves are available for use by the plumbing industry. Such valves are used in high rise buildings in order to reduce excessively high pressures found in the water supply system at the lower floors. Installation of such valves, with its specially designed pipings, fittings, added labor, instrumentation and extra required space is rather costly. For the lower floors with pressure reducing valves, a plumbing layout must be provided differing from the layout of the upper floors which have no pressure reducing valves.
Furthermore, installation of pressure reducing valves, when needed, is in addition to the routine installation of the mandated stop valve, commonly called "Stop". This Stop is usually installed at an easily accessible location, near faucets, other plumbing fixtures or equipment to facilitate servicing without shutting off other installations.
High water pressure is provided by pumps at the base of high rise buildings so that water can reach the roof tanks or upper floors. Thus, when lower floors of a high rise building are served by the same water supply system as the upper floors, the lower floors are exposed to excessively high water pressures. Maximum acceptable water pressures at plumbing fixtures are specified in building and plumbing codes in order to prevent accidents, to extend the useful life of installations and to conserve water and energy. Pressure reducing valves are available for all ranges of pressure, both incoming and outgoing, and it is essential that they hold the reduced pressure also at no flow condition.
For convenience in the text, the abbreviation PRV stands for Pressure Reducing or Regulating Valve.
The operational properties of the various available types of PRVs meet the requirements of a wide range of application and installation methods. PRVs with the necessary accessories, are installed either in branch lines near points of water consumption (faucets or outlets) or at distant stations to serve a whole zone. Each zone, consisting of one or several floors, is served by a separate water supply system and such stations are at time equipped with extensive instrumentation, including alarm systems.
For purposes of maintenance of PRVs, another valve the "Shut-Off" valve (sometimes more than one) is installed in the pipe lines. Thus, not only is accessible space required for the PRV but additional approachable space is also needed for the shut-off valve with all its connecting pipings and fittings.
When PRVs are installed in stations, space must be provided there for bypasses, shut-offs, instrumentation and alarm systems. When installed in branch lines, near points of water consumption, space has to be provided in walls, ceilings or cabinets behind access doors.
Installation of any type PRV, therefore, must take into consideration some or all of the following necessities: Special layout for the plumbing system; additional space requirements; additional labor for installations; additional pipings, fittings, instrumentation; provisions for easy access.
Also relevant is that the application of the presently available PRVs requires consideration of the mechanical and hydraulic features. In PRV stations, the number of floors must be limited because of the high hydraulic energy loss in all PRVs. Should there be a failure, a whole zone is thus effected. If installed in branch lines, these problems cannot arise.
As for individual PRVs installed near points of water consumption or in branch lines, such PRVs are usually located behind access doors in walls or in ceilings; most often, they are difficult to reach for adjustment or servicing.
With limited success, improvements have been made for installation near the point of water consumption in water supply lines by combination of PRV and Shut-Off Valves in conventional small sizes. Such combinations, however, have two bonnets and one valve body; one bonnet to reduce water pressure and the other to shut off the water. Because the bonnets are placed on opposite sides of the valve body, or placed side by side in a double body, the dimensions are by necessity quite large and still costly to install. Extended accessible space is still required for installation and servicing, as well as special plumbing layout and special labor.
For fire stand pipes and hose lines, globe and anglebody single bonnet combination pressure reducing valves exist. Due, however, to their special design features, an adaptation, such as a mere reduction in size, would not make them suitable for installation and service in potable water pipelines.